Childhood cancer mutagenesis caused by a domesticated DNA transposase

Genomic rearrangements are a hallmark of most solid tumors, including medulloblastoma, one of the most common brain tumors in children. Childhood cancers involve dysregulated cell development, but their mutational causes remain largely unknown. One of the most common forms of medulloblastoma is caused by ectopic activation of Sonic Hedgehog (SHH) signaling in cerebellar granule cell progenitors, associated with genetic deletions, amplifications, and other oncogenic chromosomal rearrangements. Here, we show that PiggyBac Transposable Element Derived 5 (Pgbd5) promotes tumor development in multiple developmentally-accurate mouse models of SHH medulloblastoma. Most mice with Pgbd5 deficiency do not develop tumors, while Pgbd5 -deficient mice maintain largely normal cerebellar development. Mouse medulloblastomas expressing Pgbd5 exhibit significantly increased numbers of somatic structural DNA rearrangements, with PGBD5-specific transposon sequences at their breakpoints. Similar sequence breakpoints recurrently affect somatic DNA rearrangements of known tumor suppressors and oncogenes in medulloblastomas in 329 children. Therefore, this study identifies PGBD5 as a primary medulloblastoma mutator and provides a genetic mechanism responsible for the generation of somatic oncogenic DNA rearrangements in childhood cancer. One-Sentence Summary Induction of somatic oncogenic mutations by the DNA transposase PGBD5 in cerebellar progenitor cells promotes medulloblastoma development. ### Competing Interest Statement The authors have declared no competing interest.